Narrative:

We were cleared by center to intercept a victor arwy, and then descend and maintain 10000'. Then center said radar lost, and that we were cleared for the ILS 12 arc approach at bzn. While establishing ourselves on the 14 DME arc, and after tuning in the localizer, we noticed that the deviation needle was pegged to the left. At that time, I descended and immediately turned to the left toward the localizer needle. We were unsure of the terrain and exactly how far to the right of course we were, so we decided to go back up to the last assigned altitude of 10000' until intercepting the localizer. I, the first officer was flying the aircraft. The captain doesn't remember telling bzn flight station at bzn that we were out of 9000'. Things were happening so fast because we were so busy flying the arc and setting up the radios. We did not know that center cleared another aircraft down to 10000'. I feel that center should not clear aircraft down to altitudes that might conflict with traffic on the approach. What is one supposed to do if in the same position, continue descending or go backup where it is safe, like we did? Also, air carrier Y airlines aircraft did the same thing a short time later, and requested another approach because they were too high. Supplemental information from acn 165940: we overshot the localizer course and found ourselves to the west of course. I directed him to continue a left turn to intercept the localizer and level off at 10000'. We both felt 10000' was a safe altitude to avoid the terrain. I informed bzn radio of our altitude and position. Bzm acknowledged and then a little while later directed a descent to 9000'.

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Original NASA ASRS Text

Title: ACR MLG STARTED DESCENT ON AN ARC FOR AN IAP ILS APCH TO BZN, THEN CLIMBED BACK TO PREVIOUS ALT WHEN THEY OVERSHOT THE LOCALIZER AND LOST SPATIAL ORIENTATION. FLT CREW FAILED TO ADVISE ATC AND ATC HAD CLEARED ANOTHER ACFT THAT WAS IN TRAIL TO THAT ALT.

Narrative: WE WERE CLRED BY CENTER TO INTERCEPT A VICTOR ARWY, AND THEN DSND AND MAINTAIN 10000'. THEN CENTER SAID RADAR LOST, AND THAT WE WERE CLRED FOR THE ILS 12 ARC APCH AT BZN. WHILE ESTABLISHING OURSELVES ON THE 14 DME ARC, AND AFTER TUNING IN THE LOC, WE NOTICED THAT THE DEVIATION NEEDLE WAS PEGGED TO THE LEFT. AT THAT TIME, I DSNDED AND IMMEDIATELY TURNED TO THE LEFT TOWARD THE LOC NEEDLE. WE WERE UNSURE OF THE TERRAIN AND EXACTLY HOW FAR TO THE RIGHT OF COURSE WE WERE, SO WE DECIDED TO GO BACK UP TO THE LAST ASSIGNED ALT OF 10000' UNTIL INTERCEPTING THE LOC. I, THE F/O WAS FLYING THE ACFT. THE CAPT DOESN'T REMEMBER TELLING BZN FLT STATION AT BZN THAT WE WERE OUT OF 9000'. THINGS WERE HAPPENING SO FAST BECAUSE WE WERE SO BUSY FLYING THE ARC AND SETTING UP THE RADIOS. WE DID NOT KNOW THAT CENTER CLRED ANOTHER ACFT DOWN TO 10000'. I FEEL THAT CENTER SHOULD NOT CLR ACFT DOWN TO ALTS THAT MIGHT CONFLICT WITH TFC ON THE APCH. WHAT IS ONE SUPPOSED TO DO IF IN THE SAME POS, CONTINUE DSNDING OR GO BACKUP WHERE IT IS SAFE, LIKE WE DID? ALSO, ACR Y AIRLINES ACFT DID THE SAME THING A SHORT TIME LATER, AND REQUESTED ANOTHER APCH BECAUSE THEY WERE TOO HIGH. SUPPLEMENTAL INFO FROM ACN 165940: WE OVERSHOT THE LOC COURSE AND FOUND OURSELVES TO THE W OF COURSE. I DIRECTED HIM TO CONTINUE A LEFT TURN TO INTERCEPT THE LOC AND LEVEL OFF AT 10000'. WE BOTH FELT 10000' WAS A SAFE ALT TO AVOID THE TERRAIN. I INFORMED BZN RADIO OF OUR ALT AND POS. BZM ACKNOWLEDGED AND THEN A LITTLE WHILE LATER DIRECTED A DSNT TO 9000'.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.